In this study, the structural, electronic and optical properties of undoped and Sb3+, Nb3+ and V3+ doped defective KTaO3 compounds are investigated using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). We have calculated bond length, band gap energies and density of states for all compounds. For undoped KTaO3 compound, the lattice parameter and bond length of Ta-O are found 4.0301 angstrom and 2.0150 angstrom, respectively. Besides, all optical parameters (real and imaginary parts of dielectric function, absorption coefficient, reflectivity and refraction index) are calculated. The refractive indices and percentage reflection increase with the doping and defect. This theoretical paper motivates further future studies.